Heart disease is very serious and often requires emergency operations to save lives. A main cause of heart disease is the accumulation of plaque inside the blood vessels, which eventually occludes the blood vessels. Several treatments are available to open up the occluded vessel (e.g., balloon angioplasty, rotational atherectomy, and intravascular stents). Traditionally, surgeons have relied on X-ray fluoroscopic images that are planar images showing the external shape of the silhouette of the lumen of blood vessels to guide treatment. Unfortunately, with X-ray fluoroscopic images, there is a great deal of uncertainty about the exact extent and orientation of the stenosis responsible for the occlusion, making it difficult to find the exact location of the stenosis. In addition, though it is known that restenosis can occur at the same place, it is difficult to check the condition inside the vessels after surgery with X-ray. Intravascular imaging, on the other hand, can be a valuable tool both during interventional procedures as an aid to navigation and for intra-operative feedback and after interventional procedures for post-operative feedback regarding the results of the procedure.
Ultrasonic transducers have been utilized to visualize the inside of the blood vessels. Current ultrasonic transducer devices are mostly based on one or more stationary ultrasound transducers or rotating a single transducer in parallel to the blood vessels by means of a rotating shaft that extends along the length of the device to a motor or other rotary device located outside the patient. The ultrasonic transducer arrangements of these devices require a relatively large amount space inside the device such that overall of diameter of the device cannot be reduced to desired sizes and/or there is not sufficient room within the device to accommodate other desired components. Also, for rotating ultrasound transducer arrangements, the rotating shaft required to facilitate rotation of the ultrasound transducer causes the distal end of the device to be very stiff, which limits the ability of the device to go through tortuous vessels. Also, the high speed rotating shaft also contributes to distorted non-uniform images when imaging a tortuous path in the vasculature, which is commonly referred to as non-uniform rotational distortion (NURD).
Optical coherence tomography (OCT) has also been utilized to visualize the inside of blood vessels based on differential reflectance, but most rely on a rotating fiber optic that extends along the length of the device. This approach also has problems including, for example, implementing the spinning and scanning motion required without damaging a delicate glass or polycarbonate optical fiber. Also, with the actuator mechanism located outside the patient and tip located inside the patient, inefficiencies and control issues arise from the torque created by a long, spinning member. In that regard, remote mechanical manipulation and a long spinning element distort the image due to NURD.
Accordingly, there remains a need for improved devices, systems, and methods for controlling motion of imaging elements within an intravascular imaging device. In that regard, there remains a need for improved rotational actuators sized and shaped for implementation within intravascular imaging devices sized for introduction into human vasculature, including intravascular imaging devices having an outer diameter of 0.018″ or less.